Inline type motorcycle engines, such as four cylinder, four-stroke engines, are generally known to have high performance and low weight. As a result, a motorcycle having an inline type engine achieves a high power-to-weight ratio, especially when additional weight is shaved from other motorcycle parts including wheels, frame, etc. The engine casings and internal parts of an inline engine are typically optimized for weight savings, within a budget. In general, achieving a lower weight may result in associated higher costs for the same performance level. For example, a racing motorcycle may use titanium, magnesium, and carbon fiber parts that are expensive but that may result in significant weight reduction.
Other types of engines are also used in high performance motorcycles, including V type engines where cylinders are oriented, as the name suggests, in a “V” configuration that includes at least two opposed cylinder banks. V type engines (and inline type engines) are also used in automobiles; however, by comparison with a motorcycle engine, an automobile engine may sacrifice an optimization of power-to-weight ratio due to other considerations such as durability, etc. In the field of V configured internal combustion engines that utilize overhead camshaft(s), a customary practice may include designing the engine so that the intake ports face toward the center of the V and so that the exhaust ports face the outside of the V engine. There are several practical reasons for placing the intake ports in the middle of the V between the two cylinder banks and for placing the exhaust ports on the outside of the engine, for example so that exhaust pipes may be easily attached, etc. This standard V type orientation allows a V type engine, for example, to be efficiently packaged under the hood of an automobile and is a standard configuration for the automobile industry.
Typically, for end-driven camshafts, overhead camshafts of both heads in a V type engine are driven from the “front” of the engine, because the crank at the rear of the engine is too large in diameter to allow for mounting a small pulley used in obtaining a 2:1 reduction ratio required for driving the overhead camshafts. Driving the camshafts for both heads from the front of the engine may cause complications due to the offset required for allowing the camshaft drives to miss one another, and due to a situation where the camshafts in the heads have different lengths and rotate in opposite directions. Due to these and other factors, a typical industry configuration for V configured internal combustion engines utilizes two completely different heads, such as heads with parts orientations that are approximately a mirror image of one another. Other differences between such heads usually includes structural differences related to the above-mentioned offset in camshaft drive.
By using different heads for the opposing sides of a V configured engine, engine manufacturing costs are significantly increased. Such cost increases may be due to extra tooling, dies, fixturing, stocking, etc. Additional costs include those related to extra labor, increases in logistical complexity including additional maintainability/reliability issues, and others. A conventional V type engine design does not provide economy of scale because it does not allow for a use of the head from a single-bank engine (e.g., an inline four cylinder type) on either side of the V when building a V configured engine.
Recently, engines have been manufactured with a V configuration and having overhead camshafts driven from a center portion of the cylinder banks, such as between a second and third cylinder. Other conventional designs have been based on front-drive type camshaft configurations. Such designs have only used front drive and center drive for driving the camshafts. However, these and other conventional V type engine designs are not optimized for driving the camshafts of the opposed heads.
It is important to note that the head(s) of an engine, even those with a camshaft drive in the center, are not perfectly symmetrical. The intake valves and ports are different compared with the exhaust valves and ports. The respective head is “handed.” Conventional automotive engines have two different heads, which are mostly the same except that one is “left-handed” and the other is “right-handed.” Previous motorcycle engine derived V-8 engines have used center-drive heads, whereby a camshaft drive is configured without adding length to the engine. One advantage to this approach of using direct chain drive of the camshafts, such as by using two sprockets located along the crankshaft, is that this is perhaps the simplest and most inexpensive way to drive the camshafts. As a result, the camshafts of the two heads rotate in a same direction, one camshaft set therefore being rotated in a direction opposite to that originally intended for the head. However, with such conventional engines there are problems with different opening and closing profiles on the cam lobes, a cam chain tensioner being on the wrong side, and other problems undesirably causing the second head to have different parts compared with the first head. Such center-drive configurations are also not easily adapted for increased performance.
Conventionally, there are additional disadvantages pertaining to a use of center-drive type camshaft drive mechanisms. In particular, there has been a conflict between a desire to minimize the size of crankshaft sprockets and the desire to utilize a thick and stiff crankshaft, which has forced engine designers to compromise a given design. Since engines of a type used with a camshaft drive mechanism require a 2:1 drive ratio between the crank and the camshafts, a sprocket on the crankshaft must be half the size of sprockets on the camshaft, for a direct drive. In order to make an engine compact, the sprocket(s) on the camshafts must be as small as possible. In the aforementioned traditional designs, this compromise may result in a very small sprocket being used on the crankshaft, which weakens the crankshaft. This situation has been addressed either by using oversized sprockets on the camshafts or by making the crankshaft very small in diameter in its middle portion. The former requires extra space and the latter creates a weak crankshaft that is subject to harmonics.
Another conventional camshaft drive mechanism has been used in a center-drive type motor, where cams are driven from the front of a V-8 engine to provide a crankshaft that is able to withstand the high torque created in a V-8 configuration. However, such a design requires extra parts and/or custom parts, which makes the design expensive. It may be desirable for racing or similar high performance applications that dictate the use of a stiff crankshaft, but this solution also has the same problem as the other “direct-drive” type designs due to the camshafts of the reversed head being rotated in the wrong direction.